This invention relates to a padded shoe brake, particularly for bicycles. More generally the invention relates to a padded shoe brake capable of an improved action and having an improved structure suitable for use on all types of two-wheel light vehicles, such as bicycles, motorcycles, mopeds, and the like.
As is known, lightweight two-wheel vehicles, and bicycles especially, generally utilize brakes which are designed to exert a braking friction action on an edge portion of a wheel assembly, more specifically on the wheel rim. Such brakes have won widespread acceptance on account of their extremely low weight, and because they do not affect by their presence the wheel structure, which may include at the center, for instance, a simple hub of small diameter. Quite different is the situation with drum and disk brakes, which, while being on the one hand efficient have, on the other hand a relatively heavy and complex construction, which has to be taken into account when the center portion of the wheel is designed apart from the significant increase of the wheel overall weight.
Padded shoe brakes may be regarded as falling into two general classes. In accordance with one solution, related to the so-called "rod-control" brakes, the shoe pads are supported on a fork of inverted-U configuration, which encompasses a portion of the tire and rim assembly and carries at its ends pads or blocks extending parallel to the plane containing the wheel. Such shoe pads are, therefore, adapted to act on the inner annular portion of the rim, which is located close to and at the side of the wheel spokes. According to another solution, related to the so-called "caliper" brakes, the pads are carried on arcuate lever arms which position the pads adjacent the sides of the rim. The braking action is here provided by the simultaneous actuation, through a Bowden cable, of both lever arms carrying the braking pads.
Both of the basic technical solutions just described are carried out into pratice in the form of a number of practical variations in which, however, the principle on which the brakes are based does not change. More specifically they have advantages and disadvantages, which condition their application in each individual case. In particular, the "rod-control" brakes are very strong, have a symmetrical structure, and have long been in use, but are relatively heavy and mechanically complex. The "caliper" brakes, in the most widespread modification thereof, are light in weight and simple, but are unbalanced because they are actuated asymmetrically with respect to the wheel mid-plane. Moreover, the lever arms may interfere with the vehicle main frame as the handle bars are turned beyond a certain angle, or in the event of a fall.
However, the main drawback affecting padded shoe brakes, which is common to all of their practical embodiments currently in use, lies in the comparatively low efficiency of these brakes in their braking action on the wheel rotational speed. This inherent shortcoming is quite familiar to those skilled in the art. This is somewhat confirmed by the fact that a great number of attempts have been made heretofore to improve the braking action of the padded shoe brakes.
In actual practice, these attempts have been unsuccessful, and the utilization of padded shoe brakes has been exclusively limited, as is known, to the lightest of two-wheel vehicles, namely bicycles.
A fundamental technical reason why the efficiency of such brakes is low is due to the reduced friction area available between the pads and rim, which is in turn due to the narrow profile of the rim, which is designed to just meet the technical requirements of the wheel.
Known pads, by acting either on the sides of the rim, or alternatively on an inner annular portion thereof adjacent the wheel spokes, only have available a small area in the direction transverse to the wheel. Of course, in the circumferential direction, the available surface area is much larger, but on the one hand it is unpractical and functionally disadvantageous to adopt pads which extend over an arc of a circle and, on the other hand, it is technically and practically unacceptable, at least with light vehicles, to adopt plural pads in series with one another.
The net result is that the only technically feasible solutions, and those actually adopted heretofore, for the improvement of the padded shoe brake action have been limited to the knurling of the rim edges, improvements in the pad material, a careful adjustment of the shoe pad movement controlling elements, and an increase in the lever arms involved in controlling the shoe pads, to allow for a given applied effort an increased force applied by the pads to the rim.
Even with such improvements, however, the action of padded shoe brakes is only acceptable, as mentioned, for bicycle use.